(6R,7R)-7-[(Z)-2 (2-aminothiazol-4-yl)-2-(1-carboxy-1-methylethoxyimino)acetamido]-3-(5,6-d ihydroxy-2-methyl-2-isoindolinium)methyl-3-cephem-4-carboxylate is a compound for which the present inventors filed an application for patent and which was disclosed in Japanese Unexamined Patent Publication No. 267587/1986. It exhibits excellent antibacterial activities against Gram-negative bacteria, particularly glucose non-fermentative Gram-negative rods, for example, Pseudomonas aeruginosa, Pseudomonas cepacia, Pseudomonas maltophilia and Acinetobacter calcoaceticus, and further, exhibits strong antibacterial activities against Pseudomonas aeruginosa AKR17 which resists known cephalosporin antibiotics. Thus, it is a prospective compound practically useful as a medicine for curing infectious diseases caused by bacteria.
The present inventors have found that the sulfate of (6R,7R)-7-[(Z)-2-(2 aminothiazol-4-yl)-2-(1-carboxy-1-methylethoxyimino)acetamido]-3-(5,6-dihy droxy-2-methyl-2-isoindolinium)methyl-3-cephem-4-carboxylate or its crystalline hydrate is more stable than the noncrystalline powder of the compound. They have conducted further researches based on this discovery, and have also found that in the process for its production, (6R,7R)-7-[(Z)-2-(2-aminothiazol-4-yl)-2-(1-carboxy-1-methylethoxyimino)ac etamido]-3-(5,6-dihydroxy-2-methyl-2-isoindolinium)methyl-3-cephem-4-carbox ylate is made into a crude hydrochloride thereof or a hydrate of the hydrochloride, followed by conversion to a sulfate thereof or a hydrate of the sulfate, whereby the (6R,7R)-7-[(Z)-2-(2-aminothiazol-4-yl)-2-(1-carboxy-1-methylethoxyimino)ac etamido]-3-(5,6-dihydroxy-2-methyl-2-isoindolinium)methyl-3-cephem-4-carbox ylate sulfate or its hydrate can be isolated and purified efficiently. The present invention has been accomplished on the basis of these discoveries.